diff --git a/crypto/src/math/ec/custom/sec/SecP128R1Field.cs b/crypto/src/math/ec/custom/sec/SecP128R1Field.cs
new file mode 100644
index 000000000..ff6fb6b65
--- /dev/null
+++ b/crypto/src/math/ec/custom/sec/SecP128R1Field.cs
@@ -0,0 +1,218 @@
+using System;
+using System.Diagnostics;
+
+using Org.BouncyCastle.Math.Raw;
+
+namespace Org.BouncyCastle.Math.EC.Custom.Sec
+{
+ internal class SecP128R1Field
+ {
+ // 2^128 - 2^97 - 1
+ internal static readonly uint[] P = new uint[] { 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFD };
+ internal static readonly uint[] PExt = new uint[] { 0x00000001, 0x00000000, 0x00000000, 0x00000004, 0xFFFFFFFE,
+ 0xFFFFFFFF, 0x00000003, 0xFFFFFFFC };
+ private static readonly uint[] PExtInv = new uint[]{ 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFB,
+ 0x00000001, 0x00000000, 0xFFFFFFFC, 0x00000003 };
+ private const uint P3 = 0xFFFFFFFD;
+ private const uint PExt7 = 0xFFFFFFFC;
+
+ public static void Add(uint[] x, uint[] y, uint[] z)
+ {
+ uint c = Nat128.Add(x, y, z);
+ if (c != 0 || (z[3] == P3 && Nat128.Gte(z, P)))
+ {
+ AddPInvTo(z);
+ }
+ }
+
+ public static void AddExt(uint[] xx, uint[] yy, uint[] zz)
+ {
+ uint c = Nat256.Add(xx, yy, zz);
+ if (c != 0 || (zz[7] == PExt7 && Nat256.Gte(zz, PExt)))
+ {
+ Nat.AddTo(PExtInv.Length, PExtInv, zz);
+ }
+ }
+
+ public static void AddOne(uint[] x, uint[] z)
+ {
+ uint c = Nat.Inc(4, x, z);
+ if (c != 0 || (z[3] == P3 && Nat128.Gte(z, P)))
+ {
+ AddPInvTo(z);
+ }
+ }
+
+ public static uint[] FromBigInteger(BigInteger x)
+ {
+ uint[] z = Nat128.FromBigInteger(x);
+ if (z[3] == P3 && Nat128.Gte(z, P))
+ {
+ Nat128.SubFrom(P, z);
+ }
+ return z;
+ }
+
+ public static void Half(uint[] x, uint[] z)
+ {
+ if ((x[0] & 1) == 0)
+ {
+ Nat.ShiftDownBit(4, x, 0, z);
+ }
+ else
+ {
+ uint c = Nat128.Add(x, P, z);
+ Nat.ShiftDownBit(4, z, c);
+ }
+ }
+
+ public static void Multiply(uint[] x, uint[] y, uint[] z)
+ {
+ uint[] tt = Nat128.CreateExt();
+ Nat128.Mul(x, y, tt);
+ Reduce(tt, z);
+ }
+
+ public static void MultiplyAddToExt(uint[] x, uint[] y, uint[] zz)
+ {
+ uint c = Nat128.MulAddTo(x, y, zz);
+ if (c != 0 || (zz[7] == PExt7 && Nat256.Gte(zz, PExt)))
+ {
+ Nat.AddTo(PExtInv.Length, PExtInv, zz);
+ }
+ }
+
+ public static void Negate(uint[] x, uint[] z)
+ {
+ if (Nat128.IsZero(x))
+ {
+ Nat128.Zero(z);
+ }
+ else
+ {
+ Nat128.Sub(P, x, z);
+ }
+ }
+
+ public static void Reduce(uint[] xx, uint[] z)
+ {
+ ulong x0 = xx[0], x1 = xx[1], x2 = xx[2], x3 = xx[3];
+ ulong x4 = xx[4], x5 = xx[5], x6 = xx[6], x7 = xx[7];
+
+ x3 += x7; x6 += (x7 << 1);
+ x2 += x6; x5 += (x6 << 1);
+ x1 += x5; x4 += (x5 << 1);
+ x0 += x4; x3 += (x4 << 1);
+
+ z[0] = (uint)x0; x1 += (x0 >> 32);
+ z[1] = (uint)x1; x2 += (x1 >> 32);
+ z[2] = (uint)x2; x3 += (x2 >> 32);
+ z[3] = (uint)x3;
+
+ Reduce32((uint)(x3 >> 32), z);
+ }
+
+ public static void Reduce32(uint x, uint[] z)
+ {
+ while (x != 0)
+ {
+ ulong c, x4 = x;
+
+ c = (ulong)z[0] + x4;
+ z[0] = (uint)c; c >>= 32;
+ if (c != 0)
+ {
+ c += (ulong)z[1];
+ z[1] = (uint)c; c >>= 32;
+ c += (ulong)z[2];
+ z[2] = (uint)c; c >>= 32;
+ }
+ c += (ulong)z[3] + (x4 << 1);
+ z[3] = (uint)c; c >>= 32;
+
+ Debug.Assert(c >= 0 && c <= 2);
+
+ x = (uint)c;
+ }
+ }
+
+ public static void Square(uint[] x, uint[] z)
+ {
+ uint[] tt = Nat128.CreateExt();
+ Nat128.Square(x, tt);
+ Reduce(tt, z);
+ }
+
+ public static void SquareN(uint[] x, int n, uint[] z)
+ {
+ Debug.Assert(n > 0);
+
+ uint[] tt = Nat128.CreateExt();
+ Nat128.Square(x, tt);
+ Reduce(tt, z);
+
+ while (--n > 0)
+ {
+ Nat128.Square(z, tt);
+ Reduce(tt, z);
+ }
+ }
+
+ public static void Subtract(uint[] x, uint[] y, uint[] z)
+ {
+ int c = Nat128.Sub(x, y, z);
+ if (c != 0)
+ {
+ SubPInvFrom(z);
+ }
+ }
+
+ public static void SubtractExt(uint[] xx, uint[] yy, uint[] zz)
+ {
+ int c = Nat.Sub(10, xx, yy, zz);
+ if (c != 0)
+ {
+ Nat.SubFrom(PExtInv.Length, PExtInv, zz);
+ }
+ }
+
+ public static void Twice(uint[] x, uint[] z)
+ {
+ uint c = Nat.ShiftUpBit(4, x, 0, z);
+ if (c != 0 || (z[3] == P3 && Nat128.Gte(z, P)))
+ {
+ AddPInvTo(z);
+ }
+ }
+
+ private static void AddPInvTo(uint[] z)
+ {
+ long c = (long)z[0] + 1;
+ z[0] = (uint)c; c >>= 32;
+ if (c != 0)
+ {
+ c += (long)z[1];
+ z[1] = (uint)c; c >>= 32;
+ c += (long)z[2];
+ z[2] = (uint)c; c >>= 32;
+ }
+ c += (long)z[3] + 2;
+ z[3] = (uint)c;
+ }
+
+ private static void SubPInvFrom(uint[] z)
+ {
+ long c = (long)z[0] - 1;
+ z[0] = (uint)c; c >>= 32;
+ if (c != 0)
+ {
+ c += (long)z[1];
+ z[1] = (uint)c; c >>= 32;
+ c += (long)z[2];
+ z[2] = (uint)c; c >>= 32;
+ }
+ c += (long)z[3] - 2;
+ z[3] = (uint)c;
+ }
+ }
+}
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